| Term | Coef | SE Coef | T | P |
| Constant | 78.1667 | 0.9072 | 86.166 | 0.000 |
| pH | 2.2125 | 0.5555 | 3.983 | 0.011 |
| Conc. (mg/L) | −7.0875 | 0.5555 | −12.758 | 0.000 |
| CT (min) | 4.2000 | 0.5555 | 7.560 | 0.001 |
| pH*pH | −49.9833 | 0.8177 | −61.126 | 0.000 |
| Conc. (mg/L)*Conc. (mg/L) | 7.3667 | 0.8177 | 9.009 | 0.000 |
| CT (min)*CT (min) | −11.6583 | 0.8177 | −14.257 | 0.000 |
| pH*Conc. (mg/L) | 5.9000 | 0.7856 | 7.510 | 0.001 |
| pH*CT (min) | 0.6250 | 0.7856 | 0.796 | 0.462 |
| Conc. (mg/L)*CT (min) | 1.6750 | 0.7856 | 2.132 | 0.086 |